Engineered Wood
Products (EWP)
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Pehrson Residence
Seattle, WA
Photo: Steve Keating
Architect: Clint Pehrson
Architects
Prefabricated Wood I-Joists
Laminated Veneer Lumber (LVL)
Parallel Strand Lumber (PSL)
Prefabricated Wood I-Joists
Introduction
Prefabricated wood I-joists are made by gluing solid sawn
lumber or laminated veneer lumber (LVL) flanges to a
plywood or oriented strandboard (OSB) panel web to
produce a dimensionally stable light-weight member with
known engineering properties.
The uniform stiffness, strength, and light weight of these
prefabricated structural products makes them well suited
for longer span joist and rafter applications for both residential and commercial construction.
The "I" shape of these products gives a high strength to weight ratio. For example, wood I-joists
241mm (9-1/2") deep and 8m (26'-3") long weigh between 23kg (50 lbs.) and 32kg (70 lbs.),
depending on the flange size. This means that they can be installed manually, giving advantages in
labour and economy.
Factory-prepunched knock-out holes in the webs facilitate the installation of electrical services. The
knockout holes also provide ventilation when the joists are used in a cathedral type ceiling with no
attic above. Some manufacturers specifically offer I-joists with ventilation holes predrilled through the
web for use in cathedral ceilings.
Holes for plumbing and mechanical ductwork may be drilled easily through the web, but must be
located according to the manufacturer's recommendations.
The wide flanges allow for a good fastening surface for sheathing, and the product can be cut and
worked using common wood working tools. However, the flanges should never be notched or drilled
and all special cuts, such as bird's mouth bearing cuts, must follow the manufacturer's
recommendations.
In some areas there may be difficulty in obtaining large dimensions of solid sawn framing lumber. The
availability of wood I-joists used as floorjoists and as deep, insulated roof joists has made them a
popular product for lightweight structural members for rafter and joist applications. They are an
economical alternative to open web steel joists.
Several different types of prefabricated wood I-joists are commercially available. Each type features a
different combination of flange and web materials, and a different connection between the web and
the flanges.
The joint between the flange and the web is a critical element of member strength and is typically
protected by patent by each manufacturer.
Flanges are commonly made of laminated veneer lumber (LVL), visually graded lumber, or MSR
lumber.
The webs are made of either oriented strandboard (OSB) or plywood.
Web panel joints are glued and mated by several methods such as butting of square panel ends,
scarfing of the panel ends, and shaping of either a toothed or tongue and groove type joint. The use
of longer OSB panels is gaining acceptance as a means of lowering the number of end-to-end panel
joints in the web.
Exterior rated phenol-formaldehyde and phenol-resorcinol are the principle adhesives used for the
web to web and web to flange joints.
Figure 1: Flange to Web Joints for Wood I-Joists
Manufacture
Wood I-joists are proprietary products and the method of manufacture varies somewhat from
one manufacturer to another. A general representation of the manufacturing process is shown
in Figure 2.
Figure 2: Manufacture of Wood I-Joists
As in the manufacture of other engineered wood products, moisture control of the flange and
web material is important to ensure optimum gluing conditions, and dimensional stability of
the finished product. All material must be dry, with an equilibrium moisture content (EMC) in
the range of at least 8 percent and no more than 18 percent. It must also be conditioned to
room temperature of at least 10ºC 50ºF).
Prior to assembly, the solid sawn flange material is fingerjoined into long lengths (no butt
joints are allowed in the flanges of prefabricated wood I-joists). A groove for acceptance of the
web is routed into one face of the flange material.
The web material is cut to the size required to give the appropriate depth to the assembled
wood I-joist. The web ends that form the web joints are cut or machined as required and the
web edges that mate with the flanges are machined, shaped or crimped as required.
Adhesive is spread on the web ends to form glued web joints and adhesive is placed into the
flange routs to form a glued flange to web connection. The top and bottom flanges are of
equal specified lengths and are end aligned with one another, prior to joist assembly. The
flanges are pressed onto the long edges of the webs just after the web joints are mated to
complete assembly of the joist.
Prior to curing, the assembled joists are cut to specified lengths. The joists are generally
placed in a low temperature oven or curing environment (21 to 65ºC 70 to 150ºF)) for a
specified period to insure proper cure of the adhesive.
After curing, the product is inspected and then bundled and wrapped for temporary storage or
shipment.
Sizes Available
Prefabricated wood I-joists are manufactured in a range of sizes. Long lengths use
fingerjoining to splice flanges and butt jointing or toothed, tongue and groove or scarf
configurations to splice the webs. The actual length is limited only by transportation
restrictions to about 20m (66').
The depths of prefabricated wood I-joists range from 241mm (9-1/2") to 508mm (20") as
shown in Table 1 although special orders in depths up to 762mm (30") can be made.
Table 1 I-Joist - Standard Depths
Size (bxd)
mm
in.
241
9-1/2
292
11-1/2
302
11-7/8
318
12-1/2
356
14
406
16
457
18
508
20
Note:
1.
Refer to manufacturer's
literature for widths and
specific load bearing capacity.
Flange depths are commonly 38mm (1-1/2") and common flange widths vary from 45mm (13/4") to 89mm (3-1/2"). Web thickness varies from 9.5mm (3/8") to 12.7mm (1/2").
Prefabricated wood I-joists generally weigh from about 3kg per metre (2 lbs. per foot) to 9kg
per metre (6 lbs. per foot) for the deepest sections.
Quality Control
The expected performance of a prefabricated wood I-joist is dependent upon the quality of the
material used in its production and the quality of the production process.
Because each manufacturer is likely to use a different
material source and a different production process,
custom production procedures must be established.
Moreover, the quality of material purchased for the
manufacture of wood I-joists varies and therefore a
quality assurance program that monitors daily
production, and independent third party quality audits
conducted by an accredited certifying agency on a
regular basis are necessary.
Before commercial production begins, each
manufacturer's product must be extensively tested to
determine the engineering properties. Once production is
started, a random sample of product is frequently
selected for testing to ensure the manufacturing
materials and processes meet prescribed strength
values.
Prefabricated wood I-joists are proprietary products having engineering qualities dependent on
the materials and flange joints used and production process variables. Therefore designers and
installers follow the design guidelines as well as the installation guidelines of the individual
manufacturers.
The Canadian Construction Materials Centre (CCMC)
has issued product evaluations for many of the
prefabricated wood I-joists marketed in Canada.
In the United States, the International Conference of
Building Officials (ICBO) has published a document
titled Acceptance Criteria for Prefabricated Wood IJoists, for evaluation of these products. The Council
of American Building Officials (CABO) has issued
product evaluations for I-joists.
The recent ASTM Standard D5055, Standard Specification for Establishing and Monitoring
Structural Capacities of Prefabricated Wood I-Joists, outlines procedures for establishing
strength values and controlling the quality of prefabricated wood I-joists.
Installation
Openings can be cut through the webs of prefabricated
wood I-joists for the passage of utilities such as heat ducts
and plumbing. Manufacturers provide clear, definite
guidelines in their product catalogues for the shape (round
and rectangular), size, and location of holes in the web.
The permissible placement and size of holes is different for
each manufacturer and therefore the specific
manufacturers’ recommendations for a product should be followed.
While limited size holes can be made for ductwork and mechanical services, the location and
size must be specifically approved by the manufacturer.
Manufacturers are also specific about the use of web reinforcement or blocking at beam
supports and points of concentrated loads. Reinforcement is intended to prevent local buckling
of the web material, to minimize bearing distance at supports, and to transfer shear loads into
reaction.
Vertical transfer of loads from above at the bearing locations may require the addition of
cripples or blocking. This may be accomplished with pieces of lumber, plywood, OSB or short
sections of the I-joist itself. All blocking should be installed according to the manufacturers
recommendations.
As with all structural elements, prefabricated wood I-joists must be adequately braced during
installation. The manufacturer’s recommendations must be followed and include required
bracing to end walls or existing deck at the ends of building bays.
Most recommendations require that all hangers, blocking, rim joists, and temporary bracing be
installed before workers are allowed on the I-joists. Lateral bracing of the top flanges with 19
x 89mm (1" x 4" nom.) wood strapping, spaced at 2.4m (8') to 3.05m (10') before sheathing
is permanently attached, is typical.
Where it is necessary to suspend mechanical services from a prefabricated wood I-joist floor
or roof, precautions should be taken to ensure that concentrated loads are not passed directly
to the lower flanges. In all cases, the manufacturers’ recommendations should be followed.
Fire Safety
Fire Safety Prefabricated wood I-joists are used in light wood-frame floor and roof assemblies
for many residential and commercial buildings. Most of the leading manufacturers have
conducted fire tests and evaluations for common floor and roof assemblies to determine the
fire performance of their wood I-joist products.
These evaluations are usually done by accredited certifying agencies and are applicable only to
the specific proprietary prefabricated wood I-joist product and other assembly components
being evaluated.
Information regarding the fire performance of assemblies incorporating specific prefabricated
wood I-joists is available from the manufacturers. Such information is also available in listings
books of the accredited certifying agencies such as Underwriters' Laboratories of Canada (ULC)
or Warnock Hersey Professional Services Ltd. in Canada or Underwriters' Laboratories Inc.
(ULI) in the US.
The Fire Safety Design in Buildings book provides details on the types of buildings which can
be constructed using prefabricated wood I-joists in light frame construction while meeting fire
safety requirements.
General guidelines for prefabricated wood I-Joists:
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Manufacturers' catalogues and evaluation
reports are the primary sources of
information for design, typical installation
details, and performance characteristics.
Typical considerations needed for product
specification include: product availability,
product sizes available (i.e. depths and
lengths) availability of approved
connectors, certified fire and sound
assembly information, engineering and
technical support provided by the
manufacturer, product quality, product
warranty, product acceptance and code
approvals, and installed cost effectiveness.
It is particularly important that prefabricated wood I-joists should be protected from
the weather during job site storage and installation. Wrapping of the product for
shipment to the job site is important providing moisture protection.
Laminated Veneer Lumber (LVL)
Introduction
Laminated veneer lumber (LVL) is a layered composite of wood veneers and adhesive. Once it
is fabricated into billets of various thicknesses and widths, it can be cut at the factory into
stock for headers and beams, flanges for prefabricated wood I-joists, or for other specific
uses. Veneer thicknesses range from 2.5mm (0.10") to 4.8mm (3/16") and common species
are Douglas fir, larch, southern yellow pine and poplar.
In LVL, the grain of each layer of veneer runs in the same (long) direction with the result that
it is strong when edge loaded as a beam or face loaded as a plank. This kind of lamination is
called parallel-lamination, and it produces a material with greater uniformity and predictability
than the same dimension material made by cross-lamination.
LVL is a solid, highly predictable, uniform lumber product because natural defects such as
knots, slope of grain and splits have been dispersed throughout the material or have been
removed altogether. It is made of dried and graded veneer which is coated with waterproof
adhesives, assembled in an arranged pattern, and formed into billets by curing in a heated
press.
One leading manufacturer grades the veneers with advanced ultrasonic grading technology in
addition to visual grading. Dependent on the end use of the LVL product the ultrasonically
graded veneers are specifically located in the material to utilize efficiently the strength
characteristics if the veneer grades. For example, if the end use of the LVL product is scaffold
plank, the higher grade veneers will be placed at the outer faces of the plank.
LVL was first used during World War II to make
airplane propellers, and since the mid-1970s, has
been available as a construction product for beams
and headers where high strength, dimension
stability, and reliability are required.
Like other products made by laminating pieces of
wood together to create a structural element such as
plywood, glulam, parallel strand lumber (PSL), or
OSB/waferboard, LVL offers the advantages of
higher reliability and lower variability through defect
removal and dispersal.
The veneering and gluing process of LVL enables large members to be made from relatively
small trees thereby providing for efficient utilization of wood fibre.
Engineering standards in Canada and the US refer to LVL and parallel strand lumber (PSL)
together as structural composite lumber (SCL).
Uses
LVL is used primarily as structural framing for residential and commercial construction and is
well suited to applications where open web steel joists and light steel beams might be
considered.
Finished or architectural grade appearance is available from some manufacturers, usually at
an additional cost. However, when it is desired to use LVL in applications where appearance is
important, common wood finishing techniques can be used to accent grain and to protect the
wood surface. In finished appearance, LVL resembles plywood or lumber on the beam face.
Other uses include scaffold planking and as flange members for some proprietary
prefabricated wood I-joists.
LVL has also been used as distribution an transmission cross arms in utility structure box
shaped roadway sign posts, and as truckbed decking with hardwood face veneers.
LVL can easily be cut to length at the jobsite. The fastening and connection details and
requirements are similar to those of solid sawn lumber. However, all special cutting, notching
or drilling should be done in accordance with manufacturer recommendations.
Strength and Appearance
LVL is mainly a structural material, most often used in applications where the material is
concealed and therefore where appearance is not important. Finished or architectural grade
appearance is available from some manufacturers, usually at an additional cost.
However, when it is desired to use LVL in applications where appearance is important,
common wood finishing techniques can be used to accent grain and to protect the wood
surface. In finished appearance, LVL resembles plywood or lumber on the beam face.
Manufacture
The initial steps of manufacture of LVL are similar to those used in the manufacture of
plywood. Typically, logs are rotary peeled on a lathe to create veneer sheets from 2.5mm
(1/10") up to 4.8mm (3/16") in thickness. Veneer sheets are generally about 2640mm (104")
long by either 1320mm (52") or 660mm (26") wide.
Figure 1: Ply Orientation of LVL
The veneer sheets are dried, clipped to remove major strength reducing defects, and graded.
The sheets are cut to the required width for the billet to be produced.
The individual veneers are then assembled with the grain of all veneers running in the long
direction of the billet. End joints between individual pieces of veneer are staggered along the
length of the billet to disperse any remaining strength reducing defects. The joints may be
scarf jointed or overlapped for some distance to provide load transfer.
Figure 2: Manufacture of LVL
The veneer lengths are coated with a waterproof phenol-formaldehyde resin adhesive. The
assembled billets are subjected simultaneously to pressure to consolidate the veneers, and to
heat to accelerate curing of the adhesive. Once again, this aspect of the process is similar to
that for plywood except that rather than being in a thin flat panel shape, the LVL material is
formed into long billets up to 25m (80') in length.
Once cured, the billets are sawn to custom lengths and widths as desired for the product end
use.
Sizes
LVL is available in lengths up to 24.4m (80'), while
more common lengths are 14.6m (48'), 17m (56'),
18.3m (60') and 20.1m (66').
LVL is manufactured in thicknesses from l9mm
(3/4") to 64mm (2-1/2"). One manufacturer also
offers an 89mm (3-l/2") thickness.
The most common thickness used in construction is
45mm (1-3/4"), from which wider beams can be
easily constructed by gun-nailing the plies together on site.
LVL is manufactured in billet widths of 610mm (24") or 1220mm (48"). The desired LVL beam
depth may be cut from these billet widths. Commonly used LVL beam depths, as shown in
Table 1, are 241mm (9-1/2"), 302mm (11-7/8"), 356mm (14"), 406mm (16") and 476mm
(18-3/4"). Depths of 140mm (5-1/2"), 184mm (7-1/4") and 610mm (24") are also available.
Table 1: LVL - Standard Sizes
Size (bxd)
mm.
in.
45 x 241
1-3/4 x 9-1/2
45 x 302
1-3/4 x 11-7/8
45 x 356
1-3/4 x 14
45 x 406
1-3/4 x 16
45 x 476
1-3/4 x 18-3/4
Quality Control
The manufacture of LVL requires an in-house quality assurance
organization. Regular independent third party quality audits by a
certification organization are a required part of the
manufacturers' quality assurance program.
LVL products are tested and approved for use by the major code
and product evaluation agencies in the United States and
Canada. All manufactured LVL products which have been tested
and approved in this way should bear the seal of the certification
agency, the manufacturer, date of manufacture, grade of LVL
and reference to any applicable code or evaluation agency
approval numbers.
LVL is a proprietary product having engineering properties that
are dependent on the materials used in the manufacture and on
the product assembly and manufacturing processes. As such, it
does not meet a common standard of production. Therefore,
designers and installers should follow the design, use and installation guidelines of the
individual manufacturers.
The Canadian Construction Materials Centre (CCMC) has issued product evaluations for many
of the LVL products marketed in Canada. In the United States, most manufacturers have
obtained product evaluation reports from the Council of American Building Officials (CABO).
Currently, a standard for the specification for evaluation of structural composite lumber
products (such as LVL and PSL) is under development by ASTM. This standard will outline
procedures for establishing, monitoring and re-evaluating structural capacities of structural
composite lumber and will also detail minimum requirements for establishment of quality
control, assurance and audit.
Fire Safety
LVL is a wood-based product and will react to fire much the same as a comparable size of solid
sawn lumber or a glued-laminated beam.
The phenol-formaldehyde resin adhesive used in manufacture are inert once cured. Therefore
they do not contribute to the fire load and the strength of the bond is not adversely affected
by heat. When used in fire-rated floor or roof assemblies, the performance of LVL is similar to
solid sawn lumber or glued-laminated timber. For more detailed information regarding the fire
ratings of LVL products, contact a manufacturer.
Laminated Strand Lumber (LSL)
LSL is the latest engineered wood product to come onto the market. This revolutionary
product is used for a broad range of applications including rim board, millwork and window,
door and garage door headers, as well as for many industrial uses. New uses for this product
are still evolving, including the use of LSL for vertical members in commercial applications
where the framing member heights are long, and the wind loads are substantial.
LSL resembles oriented strandboard in appearance because like OSB, LSL is made from long
strands coming from fast-growing aspen or poplar. However, unlike OSB, the strands are
arranged parallel to the axis of the member. Like other engineered wood products like LVL and
PSL, LSL offers predictable strength, outstanding weatherability and dimensional stability that
eliminates twist and shrinkage.
General Guidelines for LVL
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LVL products are available from most major lumber dealers in Canada and the United
States. LVL products may also be ordered directly from the manufacturer.
Manufacturers' catalogues and evaluation reports are the primary sources of
information for design, typical installation details, and performance characteristics.
Typical considerations for product specification should include: product availability,
product sizes available (i.e. widths, depths & lengths), availability of connectors,
engineering and technical support provided by the manufacturer, product quality,
product warranty, product acceptance and code approval and installed cost
effectiveness.
As with any other wood product, LVL should be protected from the weather, during
jobsite storage and after installation. Wrapping of the product for shipment to the job
site is important in providing moisture protection. End and edge sealing of the product
will enhance its resistance to moisture penetration.
Parallel Strand Lumber (PSL)
Introduction
Parallel strand lumber (PSL) is a high strength
structural composite lumber product manufactured
by gluing strands of wood together under pressure.
It is a proprietary product marketed under the
trade name Parallam®.
Because it is a glued-manufactured product. PSL
can be made in long lengths but it is usually
limited to 20m (66 ft.) by transportation
constraints.
Manufactured at a moisture content of 11 percent, which is approximately the equilibrium
moisture content of wood in most service conditions, PSL is less prone to shrinking, warping
, cupping, bowing or splitting.
It is manufactured in Canada from Douglas fir and in the United States from southern pine
from wood strands from which the growth imperfections have been removed. This results in
product having consistent properties and high load carrying ability. As smaller plantation
and second growth timber finds its way into the market place to a greater extent, PSL
provides a means of ensuring the availability of a large dimension and high quality wood
product.
The manufacturing process for PSL results in a strong, consistent material that is resistant
to seasoning stresses.
Engineering standards in Canada and the US refer to PSL and laminated veneer lumber
(LVL) together as structural composite lumber (SCL).
Uses
PSL is well suited for use as beams and columns for post and
beam construction, and for beams, headers, and lintels for light
framing construction.
It is used for large members in residential construction and as
intermediate and large members in commercial building
construction.
Visually, PSL is an attractive material which is suited to
applications where finished appearance is important. It is also
suited to concealed structural applications where appearance is
not a factor.
PSL readily accepts preservative treatment and a very high
degree of penetration and therefore protection is possible.
Treated PSL should be specified for members which will be
directly exposed to high humidity conditions.
Strength and Appearance
Parallel strand lumber exhibits the dark glue line of glue-laminated timber except that the glue
lines are much more numerous.
PSL can be machined, stained, and finished using the techniques applicable to sawn lumber.
Differing slightly from the finished appearance of sawn lumber or glulam, PSL retains the rich
textures displayed by wood products used for exposed structure, as in post and beam
construction.
The appearance of PSL allows for the structural members to be designed to view so that both
functional and aesthetic design needs can be met. PSL members readily accept stain to
enhance the warmth and texture of wood.
All PSL is sanded at the tail end of the production process to ensure precise dimensions and to
provide a high quality surface for appearance.
PSL readily accepts preservative treatment and a very high degree of penetration and
therefore protection is possible. Treated PSL should be specified for members which will be
directly exposed to high humidity conditions.
Manufacture
The initial steps of PSL manufacture as shown in Figure 1 are similar to those used in the
manufacture of plywood. Logs are turned on a lathe to create veneer and the veneer sheets
are oven dried.
Figure 1: Manufacture of PSL
The veneer sheets are clipped into long narrow strands of wood up to 2.4m (8') in length and
about 13mm (1/2") in width. Major strength reducing defects are removed from the sheets.
The strands are coated completely with an exterior-type adhesive (phenol-formaldehyde),
laid-up with the strands oriented to the length of the member, and formed into a continuous
billet which is fed into a belt press. Under pressure and microwave generated heat, the glue is
cured to produce a finished continuous billet 280 x 406mm (11" x 16") in cross-section.
The billet is cross cut to desired lengths, rip sawn to produce rough stock dimensions or
custom sizes, and sanded down to finish dimensions. Larger dimensions are produced by edge
gluing billets together using techniques common to those used for the manufacture of glulam.
Sizes Available
The stock sizes available for PSL are intended to be
compatible with established wood framing materials and
standard dimensions. Stock PSL sizes for beams and
columns are shown in Table 1.
Table 1: PSL - Standard Sizes
Beam Sizes (bxd)
Column Sizes (bxd)
mm.
in.
mm.
in.
45 x 241
1-3/4 x 9-1/2
89 x 89
3-1/2 x 3-1/2
45 x 292
1-3/4 x 11-1/2
89 x 133
3-1/2 x 5-1/4
45 x 318
1-3/4 x 12-1/2
89 x 178
3-1/2 x 7
45 x 356
1-3/4 x 14
133 x 133
5-1/4 x 5-1/4
89 x 241
3-1/2 x 9-1/2
133 x 178
5-1/4 x 7
89 x 292
3-1/2 x 11-1/2
178 x 178
7x7
89 x 318
3-1/2 x 12-1/2
89 x 356
3-1/2 x 14
89 x 406
3-1/2 x 16
89 x 457
3-1/2 x 18
133 x 241
5-1/4 x 9-1/2
133 x 292
5-1/4 x 11-1/2
133 x 318
5-1/4 x 12-1/2
133 x 356
5-1/4 x 14
133 x 406
5-1/4 x 16
133 x 457
5-1/4 x 18
178 x 241
7-1/2 x 9-1/2
178 x 292
7-1/2 x 11-1/2
178 x 318
7-1/2 x 12-1/2
178 x 356
7-1/2 x 14
178 x 406
7-1/2 x 16
178 x 457
7-1/2 x 18
PSL beams are sold in thicknesses of 45mm (1-3/4"), 68mm (2-11/16"), 89mm (3-1/2"),
133mm (5-1/4"), and 178mm (7"). The smaller thicknesses can be used individually as single
plies or can be combined for multi-ply applications.
PSL can be ordered in lengths up to 20m (66 ft.). Although it can be sawn to any dimension,
its economy is maximized in uses where light to medium steel sections are practical.
High design values, a multitude of cross sections, and long lengths permit flexibility in building
design.
Quality control
The PSL manufacturing process includes tight controls on
the raw material inputs, product assembly, and finished
product properties to ensure a consistent, high quality,
reliable product. Because the process involves the removal
of strength reducing defects from the wood strands, the
main quality control procedure is the checking for consistent
density in the finished product.
PSL is a proprietary product which has been evaluated and
accepted for use by the Canadian Construction Materials
Centre (CCMC) and by the Council of American Building
Officials (CABO).
A standard for the manufacture of PSL (and other structural
composite materials such as laminated veneer lumber
(LVL)) under development by ASTM. This standard will outline procedures for establishing
monitoring and re-evaluating structural capacities of structural composite lumber and will also
detail minimum requirements for establishment of quality control, assurance and audit.
Connections
Common wood connectors appropriate to the size of
the members are used for PSL. These range from
nails and joist hangers for the smallest sections to
bolts, split rings, and shear plates for larger sized
members.
As for all wood materials and in fact all major
building materials, galvanized connections should be
used for high humidity applications.
Fire Safety
Research conducted to measure the performance of PSL when exposed to fire demonstrates
that it is appropriate for use in all applications for which solid sawn lumber and timbers are
suited.
As a result of evaluations done in Canada by the Canadian Construction Materials Center
(CCMC) and in the US by the Council of American Building Officials (CABO) PSL has been
accepted for use in Heavy Timber construction when of appropriate cross section. Like timbers
and glulam members, PSL of large cross section has proven to be resistant to fire because the
low thermal conductivity of wood retards heat penetration, and slow charring rates allow these
large members to maintain a high percentage of their original section.
The Fire Safety Design in Buildings book provides further information on building code
requirements relating to fire safety and details the minimum size requirements for Heavy
Timber construction.
General Guidelines for PSL
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Determine the load capacity required.
Select size of PSL member which will meet the required load capacity.
Ask the local distributor for technical literature and contact the manufacturer
engineering assistance is required.
Determine if PSL members will be directly exposed to weathering or high temperature
and high humidity for significant periods during the life of the structure. If so, consult
with the manufacturer for information about preservative treatment.
Check local availability for sizes and lengths.
PSL is a patented product manufactured in both Canada and the US. For additional
product information or technical information, contact MacMillan Bloedel Limited.